The behavioral effects of cocaine are crucial to its liability to be abused. All its behavioral effects merit study. CD1 mice have been trained to run in one direction around a circular runaway, receiving milk at every third circuit. Under increasing doses of cocaine the amount of running in the direction opposite to training increases until it actually exceeds the amount in the reinforced direction, but only in some mice. Others show either no, or only slight, tendency to run in the unreinforced direction at any dose of cocaine. Mice that reverse under cocaine tend to have somewhat more running in the unreinforced direction even under control conditions. The "reversing" phenomenon will be investigated to determine its relation to running under control conditions and the relative amounts of running in the 2 directions will be deliberately manipulated in mice, to see whether such training affects the response to cocaine. Methamphetamine, chlordiazepoxide, pentobarbital and chlorpromazine over full dosage range will be studied to put the cocaine effect into perspective. Finally, other strains of mice will be studied to see how general the "reversing" phenomena is among other strains of mice.